الكافي 2/1/48/6

6. Hamid ibn Ziyad has narrated from al-Hassan ibn Muhammad ibn Sama’a from Wuhayb ibn Hafs from Abu Basir from Abu Ja’far عليه السلام who has said the following: ‘One night when the Messenger of Allah stayed in ‘A’isha’s chamber she asked, “O Messenger of Allah, why do you tire yourself when Allah has already forgiven all of your past and future sins (that the pagans thought you had committed against them)?” He replied, ‘O ‘A’isha, should not I be a grateful servant?’ “The Imam said, ‘The Messenger of Allah would stand up on his toes worshipping, then Allah revealed this to him, ‘Ta. Ha (Quran 20:1) . We have not sent the Quran to make you, (Muhammad), miserable (Quran 20:2) (It is) only a reminder for those who are afraid (of disobeying Allah). (Quran 20:3) .'"